2024-08-29_PERMIT FILE - C1980007 (2)

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West Elk Mine 2.05-37 Rev. 06/05, 01/06, 03/06, 04&05/06- PR10; 01/09- MR350; 04/09- TR116; 05/09- MR354; 08/09- TR119; 5/20- MR443; 10/20- MR450; 10/21- MR456; 6/24-TR156 The computer program determines the factor of safety for slip circles of varying radii about specified points but does not automatically converge on the minimum factor of safety. In order to minimize cost, a coarse grid was initially established. The grid was then successively refined to converge on the minimum factor of safety. In most cases three to five interactions were required. Stability analysis for SG-1 was performed using a slope stability computer program entitled XSTABL5.105. The program utilizes Bishops and/or Janbus method for circular or non- circular failure. Stability Analysis Various soil states were investigated to determine the most critical condition for each embankment. The unconsolidated undrained condition, the consolidated undrained condition, and the consolidated drained condition were considered for all embankments. In the case of FW- 1 and FW-2 (formerly MB-1), for the clay material embankment, the consolidated undrained stability was critical. Both a static analysis and a seismic analysis were performed for each dam embankment. For the static analysis a fully saturated embankment was assumed. The seismic (or dynamic) analyses, assuming the same condition, in combination, are summarized in Exhibit 44. The final run for each analysis is included as a supplement to Exhibit 44. Hydrologic Protection During Construction Early in construction, prior to the disturbance of any area for surface construction, sedimentation ponds were constructed, and diversion channels to collect undisturbed surface runoff were constructed to meet specific design requirements. These channels were constructed coincidentally with the initial access road, and divert the runoff away from the disturbed areas. These structures were designed per Exhibit 44. Runoff is released from the sedimentation ponds only after sufficient settlement of suspended solids and satisfaction of the effluent standards has been achieved. Disturbance of the adjacent areas was held to a minimum. The NPDES permits were secured prior to discharging. See Exhibit 7 to this Mining and Reclamation Plan. Construction practices are geared to minimize erosion in all disturbed areas (Exhibit 43). During construction of the ST-4 crushed coal stack-tube and storage area, drainage in the area was diverted into the enlarged MB-3 pond so that the former ponds MB-2 and MB-6 could be dried in preparation for the construction of the coal storage area. Best Management Practices (BMP) were utilized during road construction associated with the Sylvester Gulch Facilities Area (PR07). BMPs were also utilized as the substation was constructed. Prior to the construction of the shafts site benches, a clear-water diversion ditch, designed to handle the peak flow from a 100-year, 24-hour storm event, was constructed. In addition, prior to removing vegetation and stripping topsoil at the shafts site benches, sediment pond SG-1 was constructed. The shafts site will naturally drain to the sediment pond, so life-of- mine sediment ditches may not be constructed immediately, but will be established as the site is developed.